Acoustic performance is an important product differentiator amongst portable cellular telephones. In addition to the traditional operation where the phone is held close to a user's mouth, the newer generation of cell phones offers hands-free speakerphone operation, both to address driving safety concerns as well convenience. A variety of techniques have been developed to detect whether the phone is operating in a close-talking or speakerphone mode. In one technique, a host processor keeps track of the current operating mode of the device based on user selection. If a user selects the speakerphone option, then the host processor sets a number of device parameters such as echo cancellation thresholds, microphone sensitivity and high audio speaker output level to optimize the performance of the device in that mode. Another technique for detecting whether the phone is operating in a close-talking or speakerphone mode utilizes the outputs of gravitational sensors. According to this technique, the processor not only keeps track of the current mode, but will also switch from one operating mode to the other based on the output from the gravitational sensors.
The desired acoustical performance varies between the close-talking and speakerphone modes of operation. For optimal performance, in the close-talking mode, the phone should have a highly directional microphone behavior and in the speakerphone mode, it should have omni-directional behavior. Using traditional microphones, realizing both the close-talking mode and speakerphone mode of operation requires the use of more than one microphone and complex electronics and/or mechanical systems to close and open the noise-canceling port.
Accordingly, there is a need for an improved microphone system which can provide both noise-canceling and omni-directional capability.